The present invention relates to electrical current control, and in particular, to light emitting diode (“LED”) control circuits and methods.
Light emitting diodes (“LEDs”) are electronic devices that emit light when a current is passed through the device. Improvements in light emitting diodes (LEDs) have allowed such devices to be used in a growing number of applications requiring a reliable low power light source. In many applications an array of LEDs are used to provide lighting. Liquid Crystal Display (“LCD”) backlight applications are one example where several strings of LEDs are driven simultaneously in parallel.
One problem associated with driving several diodes or several strings of diodes in parallel is in keeping all the LEDs at the same brightness. The LED's brightness is related to the magnitude of the current through the LED. Because they are connected in series, each LED within a string of LEDs has the same current flowing through it as all of the other LEDs in the string. However, one problem associated with LED arrays is maintaining a matched current between strings of LEDs which are connected in parallel. For example, different LEDs in an array can have varying “turn on” voltages due to normal manufacturing variances. Accordingly, if the same voltage supply is coupled across the anode and cathode terminals of an LED array, varying levels of current through each LED string will be produced. Variations in the current will, in turn, cause varying levels of brightness for each LED string.
The preset integrated circuit (IC) solution to this problem requires that each LED string couples to a pin on the IC. This type of a solution limits the number of strings that can be implemented by any single IC to the number of input pins provided by the IC. This solution requires more and more ICs as the requirement for higher number of LED strings increases. This can make many potential applications expensive and complicated.
Thus, there is a need for improved electrical current control. The present invention solves these and other problems by providing LED control circuits and methods.